With recent development in the microelectronic technique, electronic products are developing with a trend of miniaturization, light in weight, and easy to carry. COF (Chip On Flex, or Chip On Film) is a technique in which IC (integrated circuit) chips are fixed to a flexible substrate, and an additional flexible substrate is used as a carrier for encapsulating IC chips, so as to connect IC chips with circuits on the flexible substrate. COF can to an extent solve the problem of space occupation.